This section provides background information related to the present disclosure which is not necessarily prior art. This section further provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Airfoil components, such as blades and vanes, are often formed of equiaxed, directionally solidified (DS), or single crystal (SX) superalloys. Directionally solidified (DS) or single-crystal (SX) turbine airfoils have far superior creep strength, thermal fatigue resistance as well as corrosion resistance when compared to equiaxed crystal counterparts. In particular uses, DS or SX turbine airfoils have proven to have as much as nine times more relative life in terms of creep strength and thermal fatigue resistance and over three times more relative life for corrosion resistance, when compared to equiaxed crystal counter parts.
However, single crystal casting is a slow and expensive process. In the event of a change in design, a new mold has to be fabricated. Due to high melting temperature of the Nickel superalloy, often expensive ceramic molds are required. On the other band, digital manufacturing methods, if successfully applied, can make a single crystal without a mold and thus enable design change economic.
According to the principles of the present teachings, methods and apparatus are disclosed for direct writing of single crystal super alloys and metals. In one embodiment, a substrate is heated to a predetermined temperature below its melting point, and a laser is used to form a melt pool on a surface of a substrate. The substrate is positioned on a base plate, and the laser and the base plate are movable relative to each other, with the laser being used for direct metal deposition and the substrate is heated to a temperature below its melting point. A superalloy powder is introduced to the melt pool, and the temperature of the melt pool is controlled to maintain a predetermined thermal gradient on a solid and liquid interface of the melt pool so as to form a single crystal deposit on the substrate.
In accordance with this method, an apparatus is provided for direct writing of single crystal super alloys and metals. In one embodiment, the apparatus comprises a laser having a power output; a base plate configured for holding a substrate thereon, a DMD bead configured to supply a stream of superalloy powder onto the substrate, an induction heating source positioned to heat the substrate on the base plate to a predetermined temperature, and a controller for controlling the power output of the laser to maintain the predetermined temperature. The controller is responsive to a measured temperature of at least one of a melt pool on the substrate and the superalloy powder.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.